Sirmium in the context of "Syrmia"

Béla III (Hungarian: III. Béla, Croatian: Bela III., Slovak: Belo III.; c. 1148 – 23 April 1196) was King of Hungary and Croatia between 1172 and 1196. He was the second son of King Géza II and Géza's wife, Euphrosyne of Kiev. Around 1161, Géza granted Béla a duchy, which included Croatia, central Dalmatia and possibly Sirmium. In accordance with a peace treaty between his elder brother, Stephen III, who succeeded their father in 1162, and the Byzantine Emperor Manuel I Komnenos, Béla moved to Constantinople in 1163. He was renamed to Alexios, and the emperor granted him the newly created senior court title of despotes. He was betrothed to the Emperor's daughter, Maria. Béla's patrimony caused armed conflicts between the Byzantine Empire and the Kingdom of Hungary between 1164 and 1167, because Stephen III attempted to hinder the Byzantines from taking control of Croatia, Dalmatia and Sirmium. Béla-Alexios, who was designated as Emperor Manuel's heir in 1165, took part in three Byzantine campaigns against Hungary. His betrothal to the emperor's daughter was dissolved after her brother, Alexios, was born in 1169. The emperor deprived Béla of his high title, granting him the inferior rank of kaisar.

Stephen III died on 4 March 1172, and Béla decided to return to Hungary. Before his departure, he pledged that he would never make war against the Byzantine Empire. Although the Hungarian prelates and lords unanimously proclaimed Béla king, Lucas, Archbishop of Esztergom opposed his coronation because of Béla's alleged simony. Finally, the Archbishop of Kalocsa crowned him king on 18 January 1173, with Pope Alexander III's approval. Béla fought with his younger brother, Géza, whom he held in captivity for more than a decade. Taking advantage of the internal conflicts in the Byzantine Empire after Emperor Manuel's death, Béla reoccupied Croatia, Dalmatia and Sirmium between 1180 and 1181. He occupied the Principality of Halych in 1188, but it was lost within two years.

The Roman army (Latin: exercitus Romanus) served ancient Rome and the Roman people, enduring through the Roman Kingdom (753–509 BC), the Roman Republic (509–27 BC), and the Roman Empire (27 BC – AD 476/1453), including the Western Roman Empire (collapsed AD 476/480) and the Eastern Roman Empire (collapsed AD 1453). It is thus a term that broadly spans approximately 2,206 years, during which the force underwent numerous permutations in size, composition, organization, equipment and tactics, while conserving a core of lasting traditions.

The Gepids (Latin: Gepidae, Gipedae; Ancient Greek: Γήπαιδες, romanized: Gḗpaides) were an East Germanic tribe who lived in the area of modern Romania, Hungary, and Serbia, roughly between the Tisza, Sava, and Carpathian Mountains. They were said to share the religion and language of the Goths and Vandals.

They are first mentioned by Roman sources in the third century. In the fourth century, they were among the peoples incorporated into the Hunnic Empire, within which they formed an important part. After the death of Attila, the Gepids under their leader Ardaric, led an alliance of other peoples who had been in the empire, and defeated the sons of Attila and their remaining allies at the Battle of Nedao in 454. The Gepids and their allies subsequently founded kingdoms on the Middle Danube, bordering on the Roman Empire. The Gepid Kingdom was one of the most important and long-lasting of these, centered on Sirmium, and sometimes referred to as Gepidia. It covered a large part of the former Roman province of Dacia, north of the Danube, and compared to other Middle Danubian kingdoms it remained relatively uninvolved with Rome.

The praetorian prefecture of Illyricum (Latin: praefectura praetorio per Illyricum; Greek: ὑπαρχία τῶν πραιτωρίων τοῦ Ἰλλυρικοῦ, also termed the prefecture of Illyricum) was one of four praetorian prefectures into which the Late Roman Empire was divided.

The administrative center of the prefecture was Sirmium from 375 to 379, then Thessalonica. The prefecture took its name from the older province of Illyricum, which in turn was named after ancient Illyria. In its greatest expanse it encompassed Pannonia, Noricum, Crete, and most of the Balkan peninsula except for Thrace.

The territory of the modern state of Serbia was part of the Roman Empire and later the Eastern Roman Empire. In particular, the region of Central Serbia was under Roman rule for about 800 years (with interruptions), starting from the 1st century BC, interrupted by the arrival of the Slavs into the Balkans during the 6th century, but continued after fall of the First Bulgarian Empire in the early 11th century and permanently ended with the rise of the Second Bulgarian Empire in the late 12th century. The territories were administratively divided into the provinces of Moesia (later Moesia Superior), Pannonia (later Pannonia Inferior) and Dardania. Moesia Superior roughly corresponds to modern Serbia proper; Pannonia Inferior included the eastern part of Serbia proper; Dardania included the western part of Serbia proper. After its reconquest from the Bulgarians by Emperor Basil II in 1018, it was reorganized into the Theme of Bulgaria.

The Danube River influenced the extension of the Roman Empire; its confluents, such as Sava and Morava, affected the growth of frontier fortresses and towns. Many authors and explorers wrote about traces of the Roman Empire on the Danube coast. One of the localities, Felix Romuliana, was ranked on the list of cultural heritage of UNESCO in July 2007.

The Avar–Byzantine wars were a series of conflicts between the Byzantine Empire and the Avar Khaganate. The conflicts were initiated in 568, after the Avars arrived in Pannonia, and claimed all the former land of the Gepids and Lombards as their own. This led to an unsuccessful attempt to seize the city of Sirmium from Byzantium, which had previously retaken it from the Gepids. Most subsequent conflicts came as a result of raids by the Avars, or their subject Slavs, into the Balkan provinces of the Byzantine Empire.

The Avars usually raided the Balkans when the Byzantine Empire was distracted elsewhere, typically in its frequent wars with the Sassanid Empire in the East. As a result, they often raided without resistance for long periods of time, before Byzantine troops could be freed from other fronts to be sent on punitive expeditions. This happened during the 580s and 590s, where Byzantium was initially distracted in the Byzantine–Sasanian War of 572–591, but then followed up by a series of successful campaigns that pushed the Avars back.

Stephen III (Hungarian: III. István, Croatian: Stjepan III.; Slovak: Štefan III.; summer of 1147 – 4 March 1172) was King of Hungary and Croatia between 1162 and 1172. He was crowned king in early June 1162, shortly after the death of his father, Géza II. However, his two uncles, Ladislaus and Stephen, who had joined the court of the Byzantine Empire, challenged his right to the crown. Only six weeks after his coronation, the Byzantine Emperor Manuel I Komnenos launched an expedition against Hungary, forcing the Hungarian lords to accept Ladislaus' rule. Stephen sought refuge in Austria, but returned and seized Pressburg (now Bratislava in Slovakia). Ladislaus, who died on 14 January 1163, was succeeded by Stephen's younger uncle and namesake, Stephen IV, without resistance, but his rule was unpopular. The young Stephen defeated his uncle on 19 June 1163 and expelled him from Hungary.

Stephen IV attempted to regain his throne with Emperor Manuel I's support, but the latter made peace with Stephen III. He agreed to send his younger brother, Béla, to Constantinople and to allow the Byzantines to seize Béla's duchy, which included Croatia, Dalmatia and Sirmium. In an attempt to recapture these territories, Stephen III waged wars against the Byzantine Empire between 1164 and 1167, but could not defeat the Byzantines.

Pannonia Secunda was one of the provinces of the Roman Empire. It was formed in 296 AD, during the reign of Emperor Diocletian. The capital of the province was Sirmium (today Sremska Mitrovica). Pannonia Secunda comprised parts of present-day Serbia, Croatia, and Bosnia and Herzegovina.